In the WiBro (Wireless Broadband Internet) which is a korean wireless portable internet standard, the OFDM (Orthogonal Frequency Division Multiplexing) is used as a signal transmission scheme so as to provide the high speed data service in the radio environment when a user moves. In addition, the OFDMA (Orthogonal Frequency Division Multiple Access) which is based on the OFDM is used as a multiple access scheme so that multi users might simultaneously receive an internet service. The TDD (Time Division Duplexing) which classifies the downlink and the uplink according to a time is used as a duplexing scheme.
In such a wireless telecommunication system supporting the OFDM and/or OFDMA, in order to perform a smooth communications between a base station and a terminal, the characteristic of a channel which is mutually formed should be known. For this, firstly, the synchronization has to be mutually made. Further, the operation of an oscillator has to be exact.
However, in case of the receiving side, the time offset and the carrier frequency offset can be generated due to various factors such as a multi path characteristic between the receiving side and the transmission side, and the time-varying characteristic which is generated as the terminal or the electric wave obstacle moves. Therefore, the receiving side should continuously estimate and compensate the time offset and the carrier frequency offset. Ultimately, the receiving side should estimate and compensate the channel which is mutually formed based on this.
In the meantime, in a MIMO (Multiple Input Multiple Output) system which performs the multiple input and multiple output transmission by using a plurality of transmitting antennas and a plurality of receiving antennas, a plurality of channels exist between the transmission side and the receiving side. As to the plurality of channels, even in case of the channel which is formed between the fixed transmission side and the fixed receiving side, the subcarrier which is used in channel can be changed with time (specifically, OFDMA symbol) according to the subchannel mapping rule.
Therefore, in case of the uplink PUSC mode of the MIMO system, it is necessary for the base station (receiving side) to flexibly estimate and compensate a channel according to the situation after receiving the signal transmitted with a different pilot pattern from each terminal (transmission side).